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Institute
Granitoids of the Slavkov Domain of the Brunovistulian microcontinent (BVM) in the Czech Republic have Ediacaran U-Pb zircon crystallization ages with the dominant magmatic activity occurring between ca. 597 and 595 Ma. The ages overlap published ages for the adjacent Thaya Domain, showing that both domains formed coevally in the same subduction setting. The data support published models in which the Slavkov Domain formed as arc crust. The main stage of magmatism stopped after ca. 595-590 Ma and was quickly followed by cooling accompanied by intrusion of small volumes of rhyolite dykes at ca. 594 Ma. Slavkov Domain metasedimentary rocks are dominated by Cryogenian-Ediacaran detrital zircon populations and their protoliths were locally derived erosional products of Cryogenian to Ediacaran arc rocks of the Thaya and Slavkov domains. Metasedi-mentary rocks from the NE part of the BVM contain younger, ca. 550 Ma zircons indicating that the BVM grew northeastward by accretion of progressively younger material derived from magmatic rocks with latest Ediacaran crystallization ages. In contrast to the Thaya and Slavkov domains, the Metavolcanic Zone that lies between them formed between ca. 740 and 725 Ma in the late Tonian to early Cryogenian. It predates the main stage magmatic activity in the BVM by 135 to 150 Ma and is probably a relic of older crust that formed during rifting of the Rodinia supercontinent. At ca. 552-551 Ma in the latest Ediacaran, parts of the BVM were exposed at the surface, during which time red, terrestrial siliciclastic sediments (Basal Clastics) were deposited. These largely had (very) proximal sources such as the main stage granitoids of the Thaya and Slavkov domains. Clasts of (meta)sandstones contain much older zircon populations and provide evidence that Neoarchaean and Palaeo-, meso- and early Neoproterozoic crustal rocks were exposed in erosional position nearby.
The West Burma Terrane (WBT) is a small terrane bounded to the east by the Asian Sibumasu Block and to the west by the Indo-Burman Ranges (IBR), the latter being an exhumed accretionary prism that formed during subduction of Indian oceanic lithosphere beneath Asia. Understanding the geological history of the WBT is important for reconstruction of the closure history of the Tethys Ocean and India-Asia collision. Currently there are major discrepancies in the proposed timings of collision between the WBT with both India and Asia; whether the WBT collided with India or Asia first is debated, and proposed timings of collisions stretch from the Mesozoic to the Cenozoic. We undertook a multi-technique provenance study involving petrography, detrital zircon U-Pb and Hf analyses, rutile U-Pb analyses and Sr-Nd bulk rock analyses on sediments of the Central Myanmar Basins of the WBT. We determined that the first arrival of Asian material into the basin occurred after the earliest late Eocene and by the early Oligocene, thus placing a minimum constraint on the timing of WBT-Asia collision. Our low temperature thermochronological study of the IBR records two periods of exhumation, in the early-middle Eocene, and at the Oligo-Miocene boundary. The Eocene event may be associated with the collision of the WBT with India. The later event at the Oligo-Miocene boundary may be associated with changes in wedge dynamics resulting from increased sediment supply to the system; however a number of other possible causes provide equally plausible explanations for both events.
The Big Naryn Complex (BNC) in the East Djetim-Too Range of the Kyrgyz Middle Tianshan block is a tectonized, at least 2 km thick sequence of predominantly felsic to intermediate volcanic rocks intruded by porphyric rhyolite sills. It overlies a basement of metamorphic rocks and is overlain by late Neoproterozoic Djetim-Too Formation sediments; these also occur as tectonic intercalations in the BNC. The up to ca. 1100 m thick Lower Member is composed of predominantly rhyolites-to-dacites and minor basalts, while the at least 900 m thick pyroclastic Upper Member is dominated by rhyolitic-to-dacitic ignimbrites. Porphyric rhyolite sills are concentrated at the top of the Lower Member. A Lower Member rhyolite and a sill sample have LA-ICP-MS U-Pb zircon crystallization ages of 726.1 +/- 2.2 Ma and 720.3 +/- 6.5 Ma, respectively, showing that most of the magmatism occurred within a short time span in the late Tonian-early Cryogenian. Inherited zircons in the sill sample have Neoarchean (2.63, 2.64 Ga), Paleo- (2.33-1.81 Ga), Meso- (1.55 Ga), and Neoproterozoic (ca. 815 Ma) ages, and were derived from a heterogeneous Kuilyu Complex basement. A 1751 +/- 7 Ma Ar-40/Ar-39 age for amphibole from metagabbro is the age of cooling subsequent to Paleoproterozoic metamorphism of the Kuilyu Complex. The large amount of pyroclastic rocks, and their major and trace element compositions, the presence of Neoarchean to Neoproterozoic inherited zircons and a depositional basement of metamorphic rocks point to formation of the BNC in a continental magmatic arc setting.
Late Miocene-Pliocene onset of fluvial incision of the Cauca River Canyon in the Northern Andes
(2022)
The incision of kilometer-scale canyons into high-standing topography is often used to constrain the surface uplift history of mountain ranges, controlled by tectonic and geodynamic processes.
However, changes in climate may also be responsible for canyon incision. This study deciphers the timing of incision of the similar to 2.5-km-deep Cauca River Canyon in the Central Cordillera of the Northern Andes using the cooling (exhumation) history of rocks from the canyon walls and a regional analysis of channel steepness in rivers.
Ten bedrock samples and one detrital sample were collected on the eastern border of the canyon between 300 m and 2300 m of elevation.
Bedrock and detrital AFT data yield ages from 50 to 38 Ma, while two bed-rock AHe ages from the valley bottom yield ages of 7-6 Ma.
The AHe ages and inverse thermal history models reveal a previously unidentified late Miocene (ca. 7-6 Ma) pulse of exhumation that we interpret as the age of a single incision event that formed the Cauca River Canyon.
We conclude that the Cauca River Canyon was carved as a response to rock uplift in the northern Central Cordillera and propagation of an erosion wave into the mountain range starting in the latest Miocene.
The Big Naryn Complex (BNC) in the East Djetim-Too Range of the Kyrgyz Middle Tianshan block is a tectonized, at least 2 km thick sequence of predominantly felsic to intermediate volcanic rocks intruded by porphyric rhyolite sills. It overlies a basement of metamorphic rocks and is overlain by late Neoproterozoic Djetim-Too Formation sediments; these also occur as tectonic intercalations in the BNC. The up to ca. 1100 m thick Lower Member is composed of predominantly rhyolites-to-dacites and minor basalts, while the at least 900 m thick pyroclastic Upper Member is dominated by rhyolitic-to-dacitic ignimbrites. Porphyric rhyolite sills are concentrated at the top of the Lower Member. A Lower Member rhyolite and a sill sample have LA-ICP-MS U-Pb zircon crystallization ages of 726.1 +/- 2.2 Ma and 720.3 +/- 6.5 Ma, respectively, showing that most of the magmatism occurred within a short time span in the late Tonian-early Cryogenian. Inherited zircons in the sill sample have Neoarchean (2.63, 2.64 Ga), Paleo- (2.33-1.81 Ga), Meso- (1.55 Ga), and Neoproterozoic (ca. 815 Ma) ages, and were derived from a heterogeneous Kuilyu Complex basement. A 1751 +/- 7 Ma Ar-40/Ar-39 age for amphibole from metagabbro is the age of cooling subsequent to Paleoproterozoic metamorphism of the Kuilyu Complex. The large amount of pyroclastic rocks, and their major and trace element compositions, the presence of Neoarchean to Neoproterozoic inherited zircons and a depositional basement of metamorphic rocks point to formation of the BNC in a continental magmatic arc setting.